JP7383417B2 - Acoustic wave devices and their manufacturing methods, piezoelectric thin film resonators, filters and multiplexers - Google Patents

Description

The present invention relates to an acoustic wave device, a method of manufacturing the same, a piezoelectric thin film resonator, a filter, and a multiplexer, and relates to an acoustic wave device having an inserted membrane, a method of manufacturing the same, a piezoelectric thin film resonator, a filter, and a multiplexer.

Acoustic wave devices using piezoelectric thin film resonators are used, for example, as filters and multiplexers for wireless devices such as mobile phones. A piezoelectric thin film resonator has a laminated structure in which a lower electrode and an upper electrode face each other with a piezoelectric film in between. The region where the lower electrode and the upper electrode face each other with the piezoelectric film in between is the resonance region. It is known to provide an inserted film in the piezoelectric film in the resonance region, the outer peripheral region of which is thicker than the central region (for example, Patent Document 1).

Japanese Patent Application Publication No. 2015-139167

In an acoustic wave device having a plurality of piezoelectric thin film resonators, there are cases where it is desired to have different electromechanical coupling coefficients. For example, desired filter characteristics can be obtained by making the electromechanical coupling coefficients different between the series resonator and the parallel resonator of a ladder filter. To reduce the electromechanical coupling coefficient, a capacitor is connected in parallel to the piezoelectric thin film resonator. For this reason, the elastic wave device becomes larger. Additionally, the number of manufacturing steps increases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a desired electromechanical coupling coefficient.

The present invention includes a substrate, a first lower electrode provided on the substrate, a first piezoelectric film provided on the first lower electrode, and a first piezoelectric film provided on the first piezoelectric film. a first upper electrode that faces the first lower electrode and forms a first resonant region with at least a portion of the upper electrode in between; inserted between the first lower electrode and the first upper electrode so as to surround the first central region along the outer periphery of the first resonance region in at least a part of the region surrounding the first central region. At least a portion of the first central region and a region where the first insertion film is provided, such that at least a portion of the first piezoelectric film is provided between the first insertion film and the first insertion film. a second insertion film inserted between the first insertion film and the first upper electrode; a second lower electrode provided on the substrate; a second piezoelectric film provided on the second lower electrode; and a second resonance region provided on the second piezoelectric film and facing the second lower electrode with at least a portion of the second piezoelectric film sandwiched therebetween. The second upper electrode is not provided in the second central region that is a part of the second resonant region, and is provided along the outer periphery of the second resonant region in at least a part of the region surrounding the second central region. a third insertion film inserted between the second lower electrode and the second upper electrode so as to surround the second central region; and at least one of the second piezoelectric films between the third insertion film and the third insertion film. a fourth insertion inserted between the third insertion membrane and the second lower electrode in at least a portion of the second central region and the area where the third insertion membrane is provided, such that a fourth insertion a second piezoelectric thin film resonator comprising a membrane, the thickness of the first insertion membrane and the thickness of the fourth insertion membrane are substantially equal, and the material of the first insertion membrane and the fourth insertion membrane The materials of the membranes are substantially the same, the thickness of the second insertion membrane and the thickness of the third insertion membrane are approximately equal, and the material of the second insertion membrane and the material of the third insertion membrane are approximately the same. The thickness of the first piezoelectric film between the first insertion film and the second insertion film, and the thickness of the second piezoelectric film between the third insertion film and the fourth insertion film. are substantially equal to the material of the first piezoelectric film between the first insertion film and the second insertion film and the material of the second piezoelectric film between the third insertion film and the fourth insertion film. are substantially the same, and the film thickness of the first piezoelectric film between the first lower electrode and the first insertion film and the second piezoelectric film between the second lower electrode and the fourth insertion film are approximately the same. The film thicknesses of the first piezoelectric film between the first lower electrode and the first insertion film and the second piezoelectric film between the second lower electrode and the fourth insertion film are approximately equal. The materials of the films are substantially the same, or the first piezoelectric film is not provided between the first lower electrode and the first inserted film, and the second lower electrode and the fourth inserted film are This is an acoustic wave device in which the second piezoelectric film is not provided between the second piezoelectric film and the second piezoelectric film .

In the above structure, the thickness of the first piezoelectric film between the second insertion film and the first upper electrode and the thickness of the second piezoelectric film between the third insertion film and the second upper electrode The thicknesses are substantially equal, and the material of the first piezoelectric film between the second insertion film and the first upper electrode and the material of the second piezoelectric film between the third insertion film and the second upper electrode. The materials are substantially the same, or the first piezoelectric film is not provided between the second insertion film and the first upper electrode, and the third insertion film and the second upper electrode are The second piezoelectric film may not be provided between them .

In the above structure, the main components of the first insertion film and the fourth insertion film may be the same as the main components of the second insertion film and the third insertion film.

In the above structure, the sign of the temperature coefficient of the elastic constant of the second insertion film is opposite to the sign of the elastic constant of the first piezoelectric film, and the sign of the temperature coefficient of the elastic constant of the fourth insertion film is opposite to the sign of the temperature coefficient of the elastic constant of the fourth insertion film. It is possible to have a configuration in which the sign of the elastic constant of the piezoelectric film is opposite to that of the piezoelectric film.

In the above structure, the main component of the first insertion film, the second insertion film, the third insertion film, and the fourth insertion film is silicon oxide, and the main component of the first piezoelectric film and the second piezoelectric film is silicon oxide. can be configured to be aluminum nitride.

In the above structure, a part of the first piezoelectric film is provided between the first insertion film and the first lower electrode, and the first piezoelectric film is provided between the second insertion film and the first upper electrode. A part of the second piezoelectric film is provided between the fourth insertion film and the second lower electrode, and a part of the second piezoelectric film is provided between the third insertion film and the second upper electrode. The structure may be such that a part of the second piezoelectric film is provided.

The present invention is a filter including the above elastic wave device.

The present invention is a multiplexer including the above filter.

The present invention includes a step of forming a first lower electrode and a second lower electrode on a substrate, a first piezoelectric film on the first lower electrode, and a second piezoelectric film on the second lower electrode. a first upper electrode sandwiching at least a portion of the first piezoelectric film on the first lower electrode and opposing the first lower electrode to form a first resonance region; and a second lower electrode. a second upper electrode sandwiching at least a portion of the second piezoelectric film thereon and facing the second lower electrode to form a second resonant region; The first lower electrode is not provided in a certain first central region, and is arranged so as to surround the first central region along the outer periphery of the first resonance region in at least a part of the region surrounding the first central region. and the first upper electrode, and at least a portion of the first piezoelectric film is provided between the first insertion film and the first insertion film. a second insertion film inserted between the first insertion film and the first upper electrode in a region where the first insertion film is provided; and a second insertion film that is a part of the second resonance region. The second lower electrode and the second lower electrode are not provided in the central region and are arranged so as to surround the second central region along the outer periphery of the second resonant region in at least a part of the region surrounding the second central region. at least a portion of the second central region and at least a portion of the second piezoelectric film is provided between the third insertion film and the third insertion film, a fourth insertion film inserted between the third insertion film and the second lower electrode in a region where the third insertion film is provided; The method for manufacturing an acoustic wave device includes the steps of simultaneously forming the second insertion film and the third insertion film.

According to the present invention, a desired electromechanical coupling coefficient can be achieved.

FIG. 1(a) is a plan view of the acoustic wave device according to Example 1, and FIG. 1(b) is a sectional view taken along line AA in FIG. 1(a). 2(a) and 2(b) are plan views of the insertion membrane in Example 1. 3(a) to 3(d) are cross-sectional views (part 1) showing the method for manufacturing the acoustic wave device according to the first embodiment. FIGS. 4A to 4D are cross-sectional views (part 2) showing the method for manufacturing the acoustic wave device according to the first embodiment. FIGS. 5(a) to 5(c) are cross-sectional views (part 3) showing the method for manufacturing the acoustic wave device according to the first embodiment. FIG. 6(a) is a diagram showing the diffraction intensity with respect to the diffraction angle 2θ in Experiment 1, and FIG. 6(b) is a diagram showing the FWHM of the rocking curve with respect to Rrms. 7(a) to FIG. 7(d) are cross-sectional views showing samples A to D produced in Experiment 2. FIG. 8 is a cross-sectional view of the acoustic wave device according to Example 1. FIGS. 9A to 9C are cross-sectional views of piezoelectric thin film resonators according to Modifications 1 to 3 of Example 1, respectively. FIGS. 10A and 10B are cross-sectional views of piezoelectric thin film resonators according to Modifications 4 and 5 of Example 1, respectively. FIG. 11A is a circuit diagram of a filter according to a second embodiment, and FIG. 11B is a circuit diagram of a duplexer according to a first modification of the second embodiment.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1(a) is a plan view of the acoustic wave device according to Example 1, and FIG. 1(b) is a sectional view taken along line AA in FIG. 1(a). FIG. 1A mainly shows the substrate 10, lower electrodes 12a and 12b, and upper electrodes 16a and 16b. 2(a) and 2(b) are plan views of the insertion membrane in Example 1. FIG. 2(a) mainly shows the insertion membranes 28a and 28b, and FIG. 2(b) mainly shows the insertion membranes 26a and 26b.

As shown in FIGS. 1A to 2B, piezoelectric thin film resonators 11a and 11b are provided on a substrate 10. As shown in FIGS. The piezoelectric thin film resonator 11a (first piezoelectric thin film resonator) includes a void 30a (first void), a lower electrode 12a (first lower electrode), a piezoelectric film 14a (first piezoelectric film), an upper electrode 16a (first upper (electrode), an insertion membrane 26a (first insertion membrane), and an insertion membrane 28a (second insertion membrane). The piezoelectric thin film resonator 11b (second piezoelectric thin film resonator) includes a void 30b (second void), a lower electrode 12b (second lower electrode), a piezoelectric film 14b (second piezoelectric film), an upper electrode 16b (second upper (electrode), an insertion membrane 26b (fourth insertion membrane), and an insertion membrane 28b (third insertion membrane).

On the substrate 10, a lower electrode 12a is provided with a gap 30a in between, and a lower electrode 12b is provided with a gap 30b in between. The substrate 10 is, for example, a silicon substrate. The voids 30a and 30b function as acoustic reflective layers that reflect the elastic waves excited in the piezoelectric films 14a and 14b. The lower electrodes 12a and 12b are, for example, a chromium (Cr) film and a ruthenium (Ru) film from the substrate 10 side.

Piezoelectric films 14a and 14b mainly composed of aluminum nitride (AlN) having C-axis orientation are provided on the lower electrodes 12a and 12b, respectively. The piezoelectric films 14a and 14b each include, from the substrate 10 side, a lower piezoelectric film 13a, an intermediate piezoelectric film 13b, and an upper piezoelectric film 13c.

Upper electrodes 16a and 16b are provided on piezoelectric films 14a and 14b, respectively. The upper electrodes 16a and 16b are, for example, a ruthenium film and a chromium film from the piezoelectric films 14a and 14b side.

In the piezoelectric thin film resonator 11a, the resonance region 50a (first resonance region) is defined by a region where the lower electrode 12a and the upper electrode 16a face each other with at least a portion of the piezoelectric film 14a in between. In the piezoelectric thin film resonator 11b, the resonance region 50b (second resonance region) is defined by a region where the lower electrode 12b and the upper electrode 16b face each other with at least a portion of the piezoelectric film 14b interposed therebetween. The resonance regions 50a and 50b have an elliptical shape, and are regions in which elastic waves in the thickness longitudinal vibration mode resonate within the piezoelectric films 14a and 14b.

Insertion films 26a and 26b are provided between the lower piezoelectric film 13a and the intermediate piezoelectric film 13b. Insert films 28a and 28b are provided between the intermediate piezoelectric film 13b and the upper piezoelectric film 13c.

In the piezoelectric thin film resonator 11a, the insertion film 26a is not provided in the central region 54a (first central region) that is a part of the resonance region 50a, but in the outer peripheral region 52a (first peripheral region) surrounding the central region 54a. ). The central region 54a is a region that includes the center (not necessarily the geometric center) of the resonant region 50a, and the outer peripheral region 52a is a region that includes the outer periphery of the resonant region 50a and runs along the outer periphery. The insertion film 28a is provided over the entire central region 54a and outer peripheral region 52a of the resonance region 50a. The insertion films 26a and 28a are mainly composed of silicon oxide, for example.

In the piezoelectric thin film resonator 11b, the insertion film 28b is not provided in the central region 54b (second central region) that is a part of the resonance region 50b, but is provided in the outer peripheral region 52b (second outer peripheral region) surrounding the central region 54b. ). The central region 54b is a region including the center (not necessarily the geometric center) of the resonant region 50b, and the outer peripheral region 52b is a region including the outer periphery of the resonant region 50b and along the outer periphery. The insertion film 26b is provided over the entire central region 54b and outer peripheral region 52b of the resonance region 50b. The insertion films 26b and 28b are mainly composed of silicon oxide, for example.

By providing the insertion films 26a and 28b in at least a portion of the outer peripheral regions 52a and 52b of the resonance regions 50a and 50b, it is possible to suppress leakage of elastic waves propagating in the lateral direction to the outside of the resonance regions 50a and 50b. Thereby, resonance characteristics such as Q value can be improved. By making the Young's modulus of the insertion films 26a and 28b smaller than the Young's modulus of the piezoelectric films 14a and 14b, the resonance characteristics can be further improved.

By providing the insertion films 28a and 26b in at least a portion of the central region 54a and at least a portion of the central region 54b in addition to the outer peripheral regions 52a and 52b, the frequency temperature coefficient can be reduced. By setting the sign of the temperature coefficient of the elastic constant of the insertion films 28a and 26b to be opposite to the sign of the temperature coefficient of the elastic constant of the piezoelectric films 14a and 14b, the frequency temperature coefficient can be made smaller.

Insertion films 26a and 28b may be provided so as to surround central regions 54a and 54b along the outer periphery of resonance regions 50a and 50b in at least some regions surrounding central regions 54a and 54b, respectively. The insertion films 28a and 26b may be provided in at least a portion of the central regions 54a and 54b and the region where the insertion films 26a and 28b are provided, respectively. The insertion films 26a, 26b, 28a and 28b may be provided outside the resonance regions 50a and 50b, or may not be provided outside the resonance regions 50a and 50b.

In regions where upper electrodes 16a and 16b are drawn out from resonance regions 50a and 50b, the outer periphery of resonance regions 50a and 50b is defined by the outer periphery of lower electrodes 12a and 12b. In regions where lower electrodes 12a and 12b are drawn out from resonance regions 50a and 50b, the outer periphery of resonance regions 50a and 50b is defined by the outer periphery of upper electrodes 16a and 16b.

In a region where the outer periphery of the resonance regions 50a and 50b is defined by the outer periphery of the upper electrodes 16a and 16b, the end face of the upper piezoelectric film 13c substantially coincides with the outer periphery of the upper electrodes 16a and 16b, and the end face of the upper piezoelectric film 13c substantially coincides with the outer periphery of the upper electrodes 16a and 16b, and The end face of is located outside the outer periphery of the upper electrodes 16a and 16b. The positions of the end faces of the lower piezoelectric film 13a, the intermediate piezoelectric film 13b, and the upper piezoelectric film 13c can be set as appropriate.

A protective film 24 is provided on top electrodes 16a and 16b. The protective film 24 is, for example, a silicon oxide film. A metal layer 20 is provided on the lower electrodes 12a, 12b and the upper electrodes 16a and 16b. Metal layer 20 is electrically connected to lower electrodes 12a, 12b and upper electrodes 16a and 16b. Metal layer 20 functions as a wiring and/or an electrode. The gaps 30a and 30b overlap the resonant regions 50a and 50b in a plan view, and have the same size as the resonant regions 50a and 50b or are larger than the resonant regions 50a and 50b.

As the substrate 10, in addition to a silicon substrate, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a crystal substrate, a glass substrate, a ceramic substrate, a GaAs substrate, or the like can be used. In addition to ruthenium and chromium, aluminum (Al), titanium, copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), and platinum (Pt) can be used for the lower electrodes 12a, 12b and the upper electrodes 16a and 16b. ), rhodium (Rh), iridium (Ir), etc., or a laminated film of these can be used.

In addition to aluminum nitride, the piezoelectric films 14a and 14b can be made of zinc oxide (ZnO), lead zirconate titanate (PZT), lead titanate (PbTiO ₃ ), or the like. Further, for example, the piezoelectric films 14a and 14b mainly contain aluminum nitride, and may also contain other elements to improve resonance characteristics or piezoelectricity. For example, by using scandium (Sc), two elements, a group 2 element and a group 4 element, or two elements, a group 2 element and a group 5 element, as additive elements, the piezoelectric films 14a and 14b can be will improve. Therefore, the effective electromechanical coupling coefficient of the piezoelectric thin film resonator can be improved. Group 2 elements are, for example, calcium (Ca), magnesium (Mg), strontium (Sr) or zinc (Zn). Group 4 elements are, for example, titanium, zirconium (Zr) or hafnium (Hf). Group 5 elements are, for example, tantalum, niobium (Nb) or vanadium (V). Furthermore, the piezoelectric films 14a and 14b mainly contain aluminum nitride and may also contain boron (B).

The insertion films 26a, 26b, 28a and 28b are mainly composed of silicon oxide and may contain impurities such as fluorine. For the protective film 24, an insulating film such as a silicon nitride film or an aluminum oxide film can be used instead of a silicon oxide film. The metal layer 20 is, for example, a copper layer, a gold layer or an aluminum layer.

[Production method of Example 1]
FIGS. 3(a) to 5(c) are cross-sectional views showing the method for manufacturing the acoustic wave device according to the first embodiment. As shown in FIG. 3A, a sacrificial layer 38 for forming a void on the substrate 10 having a flat main surface is formed using, for example, a sputtering method, a vacuum evaporation method, or a CVD (Chemical Vapor Deposition) method. . The thickness of the sacrificial layer 38 is, for example, 10 nm to 100 nm. The sacrificial layer 38 is made of, for example, magnesium oxide (MgO), zinc oxide (ZnO), germanium (Ge), or silicon oxide (SiO ₂ ). The sacrificial layer 38 is patterned into a desired shape using photolithography and etching. As a result, sacrificial layers 38a and 38b having desired planar shapes are formed. The shapes of sacrificial layers 38a and 38b correspond to the planar shapes of voids 30a and 30b, respectively.

The lower electrode 12 is formed on the sacrificial layers 38a, 38b and the substrate 10 using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. The lower electrode 12 is patterned into a desired shape using photolithography and etching. As a result, lower electrodes 12a and 12b having desired shapes are formed. The lower electrodes 12a and 12b may be formed by a lift-off method.

As shown in FIG. 3(b), a lower piezoelectric film 13a is formed on the lower electrodes 12a, 12b and the substrate 10 using, for example, a sputtering method or a vacuum evaporation method. As shown in FIG. 3C, the insertion film 26 is formed on the lower piezoelectric film 13a using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. As shown in FIG. 3(d), the insertion film 26 is patterned into a desired shape using photolithography and etching. Thereby, insertion films 26a and 26b are formed. The insertion films 26a and 26b may be formed using a lift-off method.

As shown in FIG. 4A, an intermediate piezoelectric film 13b is formed on the lower piezoelectric film 13a and the insertion films 26a and 26b using, for example, a sputtering method or a vacuum evaporation method. As shown in FIG. 4(b), the insertion film 28 is formed on the intermediate piezoelectric film 13b using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. As shown in FIG. 4C, the insertion film 28 is patterned into a desired shape using photolithography and etching. Thereby, insertion films 28a and 28b are formed. Insertion films 28a and 28b may be formed using a lift-off method.

As shown in FIG. 4(d), an upper piezoelectric film 13c is formed on the intermediate piezoelectric film 13b and the insertion films 28a and 28b using, for example, a sputtering method or a vacuum evaporation method. Piezoelectric films 14a and 14b are formed by the lower piezoelectric film 13a, the intermediate piezoelectric film 13b, and the upper piezoelectric film 13c. Insertion membranes 26a, 26b, 28a and 28b are inserted into piezoelectric membrane 14. The upper electrode 16 is formed on the piezoelectric film 14 using, for example, a sputtering method, a vacuum evaporation method, or a CVD method.

As shown in FIG. 5A, the upper electrode 16 is patterned into a desired shape using photolithography and etching. Thereby, upper electrodes 16a and 16b are formed. Upper electrodes 16a and 16b may be formed using a lift-off method. Using upper electrodes 16a and 16b as a mask, upper piezoelectric film 13c, intermediate piezoelectric film 13b, and lower piezoelectric film 13a are removed using an etching method. The intermediate piezoelectric film 13b and the lower piezoelectric film 13a are removed using the insertion films 28a and 28b as masks.

As shown in FIG. 5(b), a protective film 24 is formed to cover the lower electrodes 12a, 12b, the piezoelectric films 14a, 14b, the insertion films 26a, 26b, 28a, 28b, and the upper electrodes 16a, 16b. The protective film 24 is patterned into a desired shape using photolithography and etching.

As shown in FIG. 5C, a metal layer 20 is formed on the lower electrodes 12a and 12b and the upper electrodes 16a and 16b using, for example, a plating method, a sputtering method, or a vacuum evaporation method.

After that, the sacrificial layer 38 is removed using an etching solution. Gaps 30a and 30b having dome-shaped bulges are formed between lower electrodes 12a and 12b and substrate 10, respectively. As a result, the piezoelectric thin film resonators 11a and 11b shown in FIGS. 1(a) and 1(b) are manufactured.

[Experiment 1]
The electromechanical coupling coefficient of piezoelectric thin film resonators 11a and 11b depends on the crystallinity (for example, orientation) of piezoelectric films 14a and 14b. If the piezoelectric films 14a and 14b have poor crystallinity, the electromechanical coupling coefficient will be low, and if the piezoelectric films 14a and 14b have good crystallinity, the electromechanical coupling coefficient will become high. Therefore, the crystallinity of the piezoelectric film 14 was evaluated relative to the surface roughness of the base film.

The sample was prepared as follows. A ruthenium film with a thickness of 200 nm was formed on a silicon substrate using a sputtering method. By reverse sputtering the surface of the ruthenium film, the surface roughness of the ruthenium film was varied for each sample. The surface roughness of the surface of the ruthenium film was measured using an atomic force microscope (AFM). The root mean square height Rrms was measured as the surface roughness. An aluminum nitride film having a thickness of about 1000 nm was formed as a piezoelectric film on the ruthenium film by sputtering. The produced aluminum nitride film was evaluated using an X-ray diffraction (XRD) method.

FIG. 6(a) is a diagram showing the diffraction intensity with respect to the diffraction angle 2θ in Experiment 1, and FIG. 6(b) is a diagram showing the FWHM of the rocking curve with respect to Rrms. As shown in Fig. 6(a), the sample with Rrms of 1.9 nm has a larger diffraction intensity of the peak on the (002) plane than the sample with Rrms of 2.5 nm, and the full width at half maximum (FWHM) small. The FWHM of the rocking curve is an index of crystallinity; when the FWHM is large, the crystallinity is poor, and when the FWHM is small, the crystallinity is good.

As shown in FIG. 6(b), the FWHM for the Rrms of the four samples is indicated by dots. The approximate straight line of the dots is shown by a broken line. As the Rrms of the surface of the ruthenium film increases, the FWHM increases (that is, the crystallinity deteriorates).

Experiment 1 shows that as the surface roughness of the base film on which the piezoelectric film is formed increases, the crystallinity of the piezoelectric film deteriorates.

[Experiment 2]
7(a) to FIG. 7(d) are cross-sectional views showing samples A to D produced in Experiment 2. As shown in FIG. 7A, in sample A, an aluminum nitride film having a thickness of about 1000 nm was formed as a piezoelectric film 14 on a silicon substrate 10 by sputtering.

As shown in FIG. 7(b), in sample B, an aluminum nitride film having a thickness of about 500 nm was formed as a lower piezoelectric film 13a on the substrate 10 using a sputtering method. A silicon oxide film having a thickness of approximately 100 nm was formed as an insertion film 26 on the lower piezoelectric film 13a using the CVD method. An aluminum nitride film having a thickness of about 500 nm was formed as the upper piezoelectric film 13c on the insertion film 26 using a sputtering method.

As shown in FIG. 7C, in sample C, a ruthenium film having a thickness of about 200 nm was formed as a lower electrode 12 on a silicon substrate 10 by sputtering. An aluminum nitride film having a thickness of about 1000 nm was formed as a piezoelectric film 14 on the lower electrode 12 using a sputtering method.

As shown in FIG. 7D, in sample D, a ruthenium film having a thickness of about 200 nm was formed as the lower electrode 12 on the substrate 10 using a sputtering method. An aluminum nitride film having a thickness of approximately 500 nm was formed as the lower piezoelectric film 13a on the lower electrode 12 using a sputtering method. A silicon oxide film having a thickness of approximately 100 nm was formed as an insertion film 26 on the lower piezoelectric film 13a using the CVD method. An aluminum nitride film having a thickness of about 500 nm was formed as the upper piezoelectric film 13c on the insertion film 26 using a sputtering method.

The FWHM of the peak rocking curve of the (002) plane of the piezoelectric film 14 and the upper piezoelectric film 13c of Samples A to D was measured. The measured FWHM is shown below.
Sample A: 1.80°
Sample B: 2.02°
Sample C: 2.89°
Sample D: 3.33°

As seen in the comparison between Samples A and B and the comparison between Samples C and D, when the insertion film 26 is inserted into the piezoelectric film 14, the crystallinity of the upper piezoelectric film 13c on the insertion film 26 deteriorates. This is considered to be because the surface roughness of the insertion film 26 formed on the lower piezoelectric film 13a becomes large. For example, when a silicon oxide film is formed on an aluminum nitride film, the aluminum oxide film becomes amorphous with many defects, so the surface roughness of the silicon oxide film increases. If an insertion film other than a silicon oxide film is inserted into the piezoelectric film 14, the surface roughness of the insertion film becomes large.

FIG. 8 is a cross-sectional view of the acoustic wave device according to Example 1. The piezoelectric film 25a with good crystallinity is shown with the same hatching as the piezoelectric films 13a to 13c in FIG. 1(b), and the piezoelectric film 25b with poor crystallinity is shown with a cross. As shown in FIG. 8, from the results of Experiment 1, the lower piezoelectric film 13a is a piezoelectric film 25a with good crystallinity. Among the intermediate piezoelectric films 13b, the portions on the insertion films 26a and 26b are piezoelectric films 25b with poor crystallinity, and the other intermediate piezoelectric films 13b are piezoelectric films 25a with good crystallinity. Among the upper piezoelectric films 13c, the portions on the insertion films 26a, 26b, 28a, and 28b are piezoelectric films 25b with poor crystallinity, and the other upper piezoelectric films 13c are piezoelectric films 25a with good crystallinity.

In the piezoelectric thin film resonator 11a, the intermediate piezoelectric film 13b in the central region 54a is a piezoelectric film 25a with good crystallinity, whereas in the piezoelectric thin film resonator 11b, the intermediate piezoelectric film 13b in the central region 54b is a piezoelectric film 25b with poor crystallinity. It is. In both piezoelectric thin film resonators 11a and 11b, the lower piezoelectric film 13a is a piezoelectric film 25a with good crystallinity, and the outer peripheral regions 52a and 52b of the intermediate piezoelectric film 13b and the upper piezoelectric film 13c are piezoelectric films 25b with poor crystallinity.

The area ratio of outer peripheral regions 52a and 52b to resonance regions 50a and 50b is very small. For example, the width of the outer circumferential regions 52a and 52b is 1/10 or less, and sometimes 1/50 or less, of the width of the resonance regions 50a and 50b. Therefore, the electromechanical coupling coefficient of piezoelectric thin film resonators 11a and 11b is mainly determined by the crystallinity of piezoelectric films 14a and 14b in central regions 54a and 54b. The proportion of the piezoelectric film 25b with poor crystallinity in the piezoelectric film 14b in the resonance region 50b (mainly the central region 54b) of the piezoelectric thin film resonator 11b is as follows: The ratio of the piezoelectric film 25b of the piezoelectric film 14a in the inner piezoelectric film 14a is larger than that of the piezoelectric film 25b having poor crystallinity. Therefore, the electromechanical coupling coefficient of the piezoelectric thin film resonator 11b is smaller than the electromechanical coupling coefficient of the piezoelectric thin film resonator 11a.

On the other hand, piezoelectric thin film resonators 11a and 11b each include insertion films 26a and 28b. Thereby, leakage of elastic waves propagating in the lateral direction to the outside of the resonance regions 50a and 50b can be suppressed, and resonance characteristics such as the Q value can be improved. Piezoelectric thin film resonators 11a and 11b each include an insert membrane 28a and 26b. This allows the frequency temperature coefficient to be reduced. As described above, piezoelectric thin film resonators 11a and 11b with good resonance characteristics, small temperature changes, and different electromechanical coupling coefficients can be formed on the same substrate without increasing the manufacturing process. Further, in order to reduce the electromechanical coupling coefficient, it is not necessary to connect a capacitor in parallel to the piezoelectric thin film resonator 11b. This allows the elastic wave device to be miniaturized.

By appropriately setting the thicknesses of the lower piezoelectric film 13a, the intermediate piezoelectric film 13b, and the upper piezoelectric film 13c, the electromechanical coupling coefficients of the piezoelectric thin film resonators 11a and 11b can be appropriately set. For example, by making the thickness of the intermediate piezoelectric film 13b larger than the thickness of the lower piezoelectric film 13a and the upper piezoelectric film 13c, it is possible to increase the difference in the electromechanical coupling coefficient between the piezoelectric thin film resonators 11a and 11b. By making the thickness of the lower piezoelectric film 13a larger than the thicknesses of the intermediate piezoelectric film 13b and the upper piezoelectric film 13c, the electromechanical coupling coefficient of the piezoelectric thin film resonators 11a and 11b can be increased. By making the thickness of the upper piezoelectric film 13c larger than the thickness of the lower piezoelectric film 13a and the intermediate piezoelectric film 13b, the electromechanical coupling coefficient of the piezoelectric thin film resonators 11a and 11b can be reduced.

The thickness of the lower piezoelectric film 13a, the intermediate piezoelectric film 13b, and the upper piezoelectric film 13c is, for example, each from 100 nm to 400 nm, and the thickness of the insertion films 26a, 26b, 28a, and 28b is, for example, from 30 nm to 100 nm, respectively.

[Modification 1 of Example 1]
FIG. 9A is a cross-sectional view of a piezoelectric thin film resonator according to Modification 1 of Example 1. As shown in FIG. 9A, in the first modification of the first embodiment, the upper piezoelectric film 13c is not provided, and the insertion films 28a and 28b are in contact with the upper electrodes 16a and 16b. In the piezoelectric thin film resonator 11a, the inside of the resonance region 50a (particularly the central region 54a) is mostly the piezoelectric film 25a with good crystallinity. Therefore, the electromechanical coupling coefficient can be increased compared to the piezoelectric thin film resonator 11a of the first embodiment.

In the piezoelectric thin film resonator 11b, the volume ratio of the piezoelectric film 25b with poor crystallinity in the resonance region 50b becomes large. Therefore, the electromechanical coupling coefficient can be reduced. By making the thickness of the intermediate piezoelectric film 13b larger than the thickness of the lower piezoelectric film 13a, the difference in electromechanical coupling coefficient between the piezoelectric thin film resonators 11a and 11b can be increased. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 2 of Example 1]
FIG. 9(b) is a cross-sectional view of a piezoelectric thin film resonator according to a second modification of the first embodiment. As shown in FIG. 9B, in the second modification of the first embodiment, the lower piezoelectric film 13a is not provided, and the insertion films 26a and 26b are in contact with the lower electrodes 12a and 12b. In the piezoelectric thin film resonator 11a, the volume ratio of the piezoelectric film 25a with good crystallinity in the resonance region 50a becomes large. Therefore, the electromechanical coupling coefficient can be increased.

In the piezoelectric thin film resonator 11b, the inside of the resonance region 50b (particularly the central region 54b) is mostly the piezoelectric film 25b with poor crystallinity. Therefore, the electromechanical coupling coefficient can be reduced. If the adhesion between the insertion film 26b and the lower electrode 12b is poor, an adhesion layer may be provided between the insertion film 26b and the lower electrode 12b. By making the thickness of the intermediate piezoelectric film 13b larger than the thickness of the upper piezoelectric film 13c, the difference in electromechanical coupling coefficient between the piezoelectric thin film resonators 11a and 11b can be increased. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 3 of Example 1]
FIG. 9(c) is a cross-sectional view of a piezoelectric thin film resonator according to a third modification of the first embodiment. As shown in FIG. 9(c), in the third modification of the first embodiment, the lower piezoelectric film 13a and the upper piezoelectric film 13c are not provided, and the insertion films 26a and 26b are in contact with the lower electrodes 12a and 12b. Membranes 28a and 28b contact upper electrodes 16a and 16b. In the piezoelectric thin film resonator 11a, most of the resonant region 50a (particularly the central region 54a) is a piezoelectric film 25a with good crystallinity. Therefore, the electromechanical coupling coefficient can be increased.

In the piezoelectric thin film resonator 11b, the inside of the resonance region 50b (particularly the central region 54b) is mostly the piezoelectric film 25b with poor crystallinity. Therefore, the electromechanical coupling coefficient can be reduced. Modification 3 of Embodiment 1 can increase the difference in electromechanical coupling coefficient between piezoelectric thin film resonators 11a and 11b compared to Embodiment 1 and Modifications 1 and 2 thereof. The other configurations are the same as those in Example 1, and their explanation will be omitted.

When the insertion films 26a and 28b are provided near the center of the piezoelectric films 14a and 14b, leakage of elastic waves in the lateral direction can be suppressed most. Therefore, by providing the lower piezoelectric film 13a and the upper piezoelectric film 13c as in the first embodiment, resonance characteristics such as the Q value can be improved compared to Modifications 1 to 3 of the first embodiment. Insertion films 28a and 26b are provided over almost the entire surface of resonance regions 50a and 50b. Therefore, if the adhesion between the insertion film 28a and the upper electrode 16a and the adhesion between the insertion film 26b and the lower electrode 12b are poor, the insertion films 28a and 26b may peel off. Therefore, by providing the lower piezoelectric film 13a and the upper piezoelectric film 13c as in Example 1, the adhesion between the insertion films 28a and 26b can be improved.

[Modification 4 of Example 1]
FIG. 10A is a cross-sectional view of an acoustic wave device according to a fourth modification of the first embodiment. As shown in FIG. 10(a), a depression is formed on the upper surface of the substrate 10. Lower electrodes 12a and 12b are formed flat on substrate 10. As a result, voids 30a and 30b are formed in the depressions of the substrate 10. The gaps 30a and 30b are formed to include resonance regions 50a and 50b. The other configurations are the same as in Example 1, and the explanation will be omitted. The gaps 30a and 30b may be formed to penetrate the substrate 10.

[Modification 5 of Example 1]
FIG. 10(b) is a cross-sectional view of an acoustic wave device according to a fifth modification of the first embodiment. As shown in FIG. 10(b), acoustic reflective films 31a and 31b are provided under lower electrodes 12a and 12b of resonance regions 50a and 50b, respectively. In the acoustic reflection films 31a and 31b, films 31c with high acoustic impedance and films 31d with low acoustic impedance are alternately provided. The film thicknesses of the films 31c and 31d are, for example, approximately λ/4 (λ is the wavelength of the elastic wave). The number of laminated films 31c and 31d can be set arbitrarily. The acoustic reflection films 31a and 31b may be formed by laminating at least two types of layers having different acoustic characteristics with an interval between them. Further, the substrate 10 may be one of at least two types of layers having different acoustic characteristics, the acoustic reflection films 31a and 31b. For example, the acoustic reflection films 31a and 31b may have a structure in which two films having different acoustic impedances are provided in the substrate 10. The other configurations are the same as in Example 1, and the explanation will be omitted.

As in Example 1 and Modifications 1 to 4 thereof, the piezoelectric thin film resonator is an FBAR (Film Bulk Acoustic Resonator) may also be used. Also, as in the fifth modification of the first embodiment, the piezoelectric thin film resonator includes an acoustic reflection film 31a that reflects elastic waves propagating through the piezoelectric films 14a and 14b below the lower electrodes 12a and 12b in the resonance regions 50a and 50b; An SMR (Solidly Mounted Resonator) equipped with 31b may also be used. The acoustic reflection layer that reflects elastic waves may include voids 30a and 30b or acoustic reflection films 31a and 31b.

In the first embodiment and its modifications, the planar shape of the resonance regions 50a and 50b has been explained using an elliptical shape as an example, but it may be a polygonal shape such as a quadrangular shape or a pentagonal shape.

According to the first embodiment and its modifications, in the piezoelectric thin film resonator 11a, the insertion film 26a (first insertion film) is inserted between the lower electrode 12a and the upper electrode 16a, and the insertion film 28a (second insertion film) is inserted between the lower electrode 12a and the upper electrode 16a. ) is inserted between the insertion film 26a and the upper electrode 16a so that at least part of the intermediate piezoelectric film 13b of the piezoelectric film 14a is provided between the insertion film 26a and the intermediate piezoelectric film 13b. The insertion film 26a is not provided in the central region 54a, but is provided so as to surround the central region 54a along the outer periphery of the resonance region 50a in at least a part of the region surrounding the central region 54a. The insertion film 28a is provided in at least a portion of the central region 54a and the region where the insertion film 26a is provided.

On the other hand, in the piezoelectric thin film resonator 11b, the insertion film 28b (third insertion film) is inserted between the lower electrode 12b and the upper electrode 16b, and the insertion film 26b (fourth insertion film) is inserted between the insertion film 28b. The piezoelectric film 14b is inserted between the insertion film 28b and the lower electrode 12b so that at least a portion of the intermediate piezoelectric film 13b is provided. The insertion film 28b is provided so as to surround the central region 54b along the outer periphery of the resonance region 50b in at least a part of the region surrounding the central region 54b. The insertion film 26b is provided in at least a portion of the central region 54b and the region where the insertion film 28b is provided.

The insertion films 26a and 28b can improve resonance characteristics such as the Q value of the piezoelectric thin film resonators 11a and 11b. The frequency-temperature characteristics of the piezoelectric thin film resonators 11a and 11b can be reduced by the insertion films 28a and 26b. Furthermore, the electromechanical coupling coefficients between the piezoelectric thin film resonators 11a and 11b can be independently set to desired values. Further, since there is no need to use a parallel capacitor to reduce the electromechanical coupling coefficient, miniaturization is possible.

As shown in FIGS. 3(c) and 3(d), insertion films 26a and 26b are formed simultaneously, and as shown in FIGS. 4(b) and 4(c), insertion films 28a and 28b are formed simultaneously. Thereby, the electromechanical coupling coefficients of the piezoelectric thin film resonators 11a and 11b can be independently set to desired values, and the manufacturing process can be simplified.

When an acoustic wave device is manufactured in this manner, the thickness of the insertion film 26a and the thickness of the insertion film 26b are approximately equal, and the material of the insertion film 26a and the material of the insertion film 26b are approximately the same. The thickness of the insertion film 28a and the thickness of the insertion film 28b are approximately equal, and the material of the insertion film 28a and the material of the insertion film 28b are approximately the same.

Further, as shown in FIG. 4A, an intermediate piezoelectric film 13b between the piezoelectric thin film resonators 11a and 11b is formed at the same time. Thereby, the electromechanical coupling coefficients of the piezoelectric thin film resonators 11a and 11b can be independently set to desired values, and the manufacturing process can be simplified.

When an acoustic wave device is manufactured in this way, the thickness of the intermediate piezoelectric film 13b between the insertion films 26a and 28a is approximately equal to the thickness of the intermediate piezoelectric film 13b between the insertion films 26b and 28b, and the insertion film The material of the intermediate piezoelectric film 13b between 26a and 28a and the material of the intermediate piezoelectric film 13b between the insertion films 26b and 28b are substantially the same. Note that the fact that the film thicknesses are substantially the same and the materials are substantially the same allows for differences of the order of manufacturing errors.

The main components of the insertion films 26a and 26b and the main components of the insertion films 28a and 28b are the same. Thereby, the insertion membranes 26a and 28b can be used as membranes for the same purpose, and the insertion membranes 28a and 26b can be used as membranes for the same purpose.

The sign of the temperature coefficient of the elastic constant of the insertion film 28a is opposite to the sign of the elastic constant of the piezoelectric film 14a, and the sign of the temperature coefficient of the elastic constant of the insertion film 26b is opposite to the sign of the elastic constant of the piezoelectric film 14b. This allows the insertion films 28a and 26b to be used as temperature compensation films.

The insertion films 28a and 26b are preferably provided over 80% or more of the area of the resonant regions 50a and 50b, respectively, and preferably over all of the resonant regions 50a and 50b. This allows the frequency temperature coefficient to be further reduced.

The Young's modulus of the insertion film 26a is smaller than the Young's modulus of the piezoelectric film 14a, and the Young's modulus of the insertion film 28b is smaller than the Young's modulus of the piezoelectric film 14b. Thereby, the insertion films 26a and 28b can further suppress leakage of horizontally propagating elastic waves from the resonance regions 50a and 50b. Therefore, the resonance characteristics of the piezoelectric thin film resonators 11a and 11b can be further improved.

The width of the insertion films 26a and 28b (the width in the direction perpendicular to the tangent to the outer periphery of the resonance regions 50a and 50b) is preferably 1/5 or less of the width of the resonance regions 50a and 50b (for example, the length of the minor axis of the ellipse). More preferably, it is 1/10 or less. Thereby, resonance characteristics can be improved. The width of the resonance regions 50a and 50b is preferably 10 times or more the wavelength of the elastic wave.

The main component of the insertion films 26a, 26b, 28a and 28b is silicon oxide, and the main component of the piezoelectric films 14a and 14b is aluminum nitride. As a result, the signs of the temperature coefficients of the elastic constants of the insertion films 28a and 26b can be made opposite to the signs of the elastic constants of the piezoelectric films 14a and 14b, and the Young's modulus of the insertion films 26a and 28b can be changed to the Young's modulus of the piezoelectric films 14a and 14b. Can be made smaller.

It should be noted that the main component is allowed to contain impurities that may be included intentionally or unintentionally, and is meant to be included to the extent that the effects of Example 1 and its modifications are achieved. For example, the piezoelectric films 14a and 14b contain nitride and aluminum in a total of 50 atom% or more or 80 atom% or more, and the insertion films 26a, 26b, 28a, and 28b contain oxide and silicon in a total of 50 atom% or more or 80 atom% or more. .

As in the first embodiment, the lower piezoelectric film 13a is provided between the insertion films 26a and 26b and the lower electrodes 12a and 12b, and the upper piezoelectric film 13c is provided between the insertion films 28a and 28b and the upper electrodes 16a and 16b. It is provided. Thereby, peeling of the insertion films 26a, 26b, 28a, and 28b can be suppressed. Furthermore, the resonance characteristics of the piezoelectric thin film resonators 11a and 11b can be improved.

As in Patent Document 1, if an inserted film is provided in the piezoelectric film in the resonance region, the outer peripheral region of which is thicker than the central region, the frequency temperature coefficient can be reduced and the resonance characteristics can be improved. However, due to problems in the manufacturing process, the intermediate piezoelectric film 13b may be provided between the insertion films 26 and 28. In this case, as in the piezoelectric thin film resonator 11a, the lower insertion film 26a is used as an insertion film to improve the resonance characteristics, and as in the piezoelectric thin film resonator 11b, the upper insertion film 28b is used as the insertion film to improve the resonance characteristics. There is a method of inserting a membrane to improve the performance.

Unlike the piezoelectric thin film resonator 11a, the insertion film 26a (first insertion film 26a) that is not provided in the central region 54a and surrounds the central region 54a along the outer periphery of the resonant region 50a in at least a part of the region surrounding the central region 54a. (film) is inserted between the lower piezoelectric film 13a and the intermediate piezoelectric film 13b. An insertion film 28a (second insertion film) provided in at least a portion of the central region 54a and the region where the insertion film 26a is provided is inserted between the intermediate piezoelectric film 13b and the upper piezoelectric film 13c. Thereby, the electromechanical coupling coefficient can be increased compared to the piezoelectric thin film resonator 11b.

Example 2 is an example of a filter and a duplexer using the piezoelectric thin film resonator of Example 1 and its modification. FIG. 11(a) is a circuit diagram of a filter according to the second embodiment. As shown in FIG. 11(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. The elastic wave device of Example 1 and its modified examples can be used for at least two resonators, one or more series resonators S1 to S4 and one or more parallel resonators P1 to P3. The number of resonators of the ladder filter can be set as appropriate.

By using the piezoelectric thin film resonator 11a as at least one of the one or more series resonators S1 to S4, the skirt characteristic on the high frequency side of the pass band of the ladder filter can be made steep. By using the piezoelectric thin film resonator 11b as the other resonator, the pass band can be widened. By using the piezoelectric thin film resonator 11a as at least one of the one or more parallel resonators P1 to P3, the skirt characteristic on the high frequency side of the passband can be made steep. By using the piezoelectric thin film resonator 11b as the other resonator, the pass band can be widened.

FIG. 11(b) is a circuit diagram of a duplexer according to a first modification of the second embodiment. As shown in FIG. 11(b), a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes signals in the transmission band among the signals input from the transmission terminal Tx to the common terminal Ant as transmission signals, and suppresses signals at other frequencies. The reception filter 42 passes signals in the reception band among the signals input from the common terminal Ant to the reception terminal Rx as reception signals, and suppresses signals at other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second embodiment.

Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention as described in the claims. Changes are possible.

10 Substrate 11a, 11b Piezoelectric thin film resonator 12, 12a, 12b Lower electrode 13a Lower piezoelectric film 13b Intermediate piezoelectric film 13c Upper piezoelectric film 14a, 14b Piezoelectric film 16, 16a, 16b Upper electrode 26, 26a, 26b, 28, 28a, 28b Insertion film 30a, 30b Gap 31a, 31b Acoustic reflection film 40 Transmission filter 42 Reception filter 50a, 50b Resonance region 52a, 52b Outer region 54a, 54b Central region

Claims (9)

A substrate and
a first lower electrode provided on the substrate; a first piezoelectric film provided on the first lower electrode; a first upper electrode that faces the first lower electrode and forms a first resonant region; a first insertion film inserted between the first lower electrode and the first upper electrode so as to surround the first central region along the outer periphery of the first resonance region in a part of the region; the first insertion film in at least a part of the first central region and the region where the first insertion film is provided, such that at least a part of the first piezoelectric film is provided between the first insertion film and the first insertion film; a first piezoelectric thin film resonator comprising: a second insertion film inserted between the first upper electrode;
a second lower electrode provided on the substrate; a second piezoelectric film provided on the second lower electrode; a second upper electrode that faces the second lower electrode and forms a second resonant region; a third insertion film inserted between the second lower electrode and the second upper electrode so as to surround the second central region along the outer periphery of the second resonant region in a part of the region; and the third insertion film in at least a part of the second central region and the region where the third insertion film is provided, such that at least a part of the second piezoelectric film is provided between the third insertion film and the second piezoelectric film. a second piezoelectric thin film resonator comprising: a fourth insertion film inserted between the second lower electrode;
Equipped with
The thickness of the first insertion membrane and the fourth insertion membrane are approximately equal, and the material of the first insertion membrane and the material of the fourth insertion membrane are approximately the same,
The thickness of the second insertion membrane and the thickness of the third insertion membrane are approximately equal, and the material of the second insertion membrane and the material of the third insertion membrane are approximately the same,
The thickness of the first piezoelectric film between the first insertion film and the second insertion film and the thickness of the second piezoelectric film between the third insertion film and the fourth insertion film are approximately Equally, the material of the first piezoelectric film between the first insertion film and the second insertion film and the material of the second piezoelectric film between the third insertion film and the fourth insertion film are approximately are the same,
The thickness of the first piezoelectric film between the first lower electrode and the first insertion film and the thickness of the second piezoelectric film between the second lower electrode and the fourth insertion film are approximately Equally, the material of the first piezoelectric film between the first lower electrode and the first insertion film and the material of the second piezoelectric film between the second lower electrode and the fourth insertion film are approximately the same, or the first piezoelectric film is not provided between the first lower electrode and the first insertion film, and the first piezoelectric film is not provided between the second lower electrode and the fourth insertion film; An acoustic wave device in which the second piezoelectric film is not provided . The thickness of the first piezoelectric film between the second insertion film and the first upper electrode and the thickness of the second piezoelectric film between the third insertion film and the second upper electrode are approximately Equally, the material of the first piezoelectric film between the second insertion film and the first upper electrode and the material of the second piezoelectric film between the third insertion film and the second upper electrode are approximately the same, or the first piezoelectric film is not provided between the second insertion film and the first upper electrode, and the first piezoelectric film is not provided between the third insertion film and the second upper electrode; The acoustic wave device according to claim 1, wherein the second piezoelectric film is not provided. The acoustic wave device according to claim 1 or 2, wherein the main components of the first insertion film and the fourth insertion film are the same as the main components of the second insertion film and the third insertion film. The sign of the temperature coefficient of the elastic constant of the second inserted film is opposite to the sign of the elastic constant of the first piezoelectric film, and the sign of the temperature coefficient of the elastic constant of the fourth inserted film is opposite to the sign of the temperature coefficient of the elastic constant of the second piezoelectric film. The elastic wave device according to any one of claims 1 to 3, wherein the sign of the constant is opposite. The main component of the first insertion film, the second insertion film, the third insertion film, and the fourth insertion film is silicon oxide,
The acoustic wave device according to any one of claims 1 to 3, wherein the main component of the first piezoelectric film and the second piezoelectric film is aluminum nitride. A part of the first piezoelectric film is provided between the first insertion film and the first lower electrode, and a part of the first piezoelectric film is provided between the second insertion film and the first upper electrode. is established,
A part of the second piezoelectric film is provided between the fourth insertion film and the second lower electrode, and a part of the second piezoelectric film is provided between the third insertion film and the second upper electrode. The acoustic wave device according to any one of claims 1 to 5, wherein the acoustic wave device is provided with: A filter comprising the elastic wave device according to any one of claims 1 to 6 . A multiplexer comprising a filter according to claim 7 . forming a first lower electrode and a second lower electrode on the substrate;
forming a first piezoelectric film on the first lower electrode and a second piezoelectric film on the second lower electrode;
a first upper electrode sandwiching at least a portion of the first piezoelectric film on the first lower electrode and opposing the first lower electrode to form a first resonance region; forming a second upper electrode that faces the second lower electrode and forms a second resonance region, sandwiching at least a portion of the piezoelectric film;
The first central region is not provided in the first central region that is a part of the first resonant region, and the first central region is provided along the outer periphery of the first resonant region in at least a part of the region surrounding the first central region. At least a portion of the first piezoelectric film is provided between a first insertion film inserted between the first lower electrode and the first upper electrode, and the first insertion film so as to surround the first piezoelectric film. a second insertion film inserted between the first insertion film and the first upper electrode in at least a part of the first central region and a region where the first insertion film is provided; It is not provided in the second central region that is a part of the resonant region, and surrounds the second central region along the outer periphery of the second resonant region in at least a part of the region surrounding the second central region. , a third insertion film inserted between the second lower electrode and the second upper electrode, and at least a part of the second piezoelectric film is provided between the third insertion film and the third insertion film; a fourth insertion film inserted between the third insertion film and the second lower electrode in at least a part of the second central region and a region where the third insertion film is provided; simultaneously forming a membrane and the fourth insertion membrane;
A method for manufacturing an acoustic wave device, comprising the step of simultaneously forming the second insertion film and the third insertion film.

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